The disclosure relates to a memory device and a method of fabricating such a memory device, and more particularly, to a resistive memory device like a nonvolatile resistive random access memory (ReRAM) device and a method of fabricating the same.
Recently, next-generation memory devices substituted for dynamic random access memory (DRAM) devices and flash memory devices have been researched.
One of the next-generation memory devices is a resistive memory device using a material capable of being switched between at least two resistance states by a sharp variance of resistances in response to a bias applied to the material. Hereafter, the material is referred to as a resistive layer. A binary oxide including a transition metal oxide or a perovskite material is used as the resistive layer.
In general, each cell in the resistive memory device has a selection element for selecting a that cell and a resistance-variable resistive element electrically connected to the selection element. A selection transistor or a selection diode is used as the selection element. In addition, the resistive element includes an upper electrode, a lower electrode and the resistive layer interposed between the upper electrode and the lower electrode.
Recently, a memory cell structure where a vertical selection diode and a resistive element are stacked one upon another has been suggested. Particularly, the vertical selection diode in the suggested structure has a binary oxide structure in which an n-type oxide such as TiO2 and a p-type oxide such as NiO are stacked one upon another.
However, using a binary oxide for the vertical selection diode causes some problems in that a current density through the diode is not sufficiently high and a rectifying characteristic through the diode is not sufficiently good for certain applications.